The present invention relates to a studless tire that assures good running performance over snow- or ice-covered road surfaces without requiring studs on the tread surface.
The use of spiked tires with studs embedded in the tread has been popular on automobiles running on snow- or ice-covered road surfaces. However, in recent years an increasing number of local governments are banning the use of spiked tires because they cause the problem of wearing the surface of bare pavement with the protruding end of studs.
Under the circumstances, the use of studless tires which assure an improvement in the running performance over snow- or ice-covered road surfaces without providing studs on the tread surface is increasing. With such studless tires, their running performance on snow- or ice-covered road surfaces is improved by providing the tread with a block pattern consisting of a plurality of blocks, with a plurality of sipes being provided in each block.
However, the performance requirements for tires to possess include starting and accelerating performance, braking performance, cornering performance and hill climbing performance and it is necessary that a good balance be attained between these performance characteristics. With conventional studless tires, however, emphasis is placed on improvements in the braking performance on snow- or ice-covered road surfaces and they cannot be said to be completely satisfactory in other aspects such as cornering performance.
Furthermore, the conventional studless tires have had the problem that their running performance on highways in a bare condition is rather poor.
To insure better grip on snow and ice surfaces, the studless tires have ends of the tread formed in square shoulders but this causes unsteady running, or "wandering", in the ruts worn in wheel tracks.
Still a further problem with studless tires which are specially designed to maintain low temperatures is that they adopt tread rubber formulations having the tendency to provide lower grip on bare pavement. A vehicle with such tires installed on wheels will experience increased understeer when it corners.
With the recent increase in the number of local governments that ban the use of spiked tires, there is a growing need for the development of studless tires having better running performance on highways in a bare condition.
An object, therefore, of the present invention is to provide a studless tire that is improved in running performance, particularly cornering performance, on snow- or ice-covered road surfaces.
Another object of the present invention is to provide a studless tire that is improved in running performance not only on snow- or ice-covered road surfaces but also on highways in a bare condition.